Hepatitis C (HCV) is an RNA single-stranded virus and member of the Hepacivirus genus. It is estimated that 75% of all cases of liver disease are caused by HCV. HCV infection can lead to cirrhosis and liver cancer, and if left to progress, liver failure that may require a liver transplant. Approximately 71 million people worldwide are living with chronic HCV infections and approximately 399,000 people die each year from HCV, mostly from cirrhosis and hepatocellular carcinoma.
RNA polymerase is a key target for drug development against RNA single stranded viruses. The HCV non-structural protein NS5B RNA-dependent RNA polymerase is a key enzyme responsible for initiating and catalyzing viral RNA synthesis. There are two major subclasses of NS5B inhibitors: nucleoside analogs and non-nucleoside inhibitors (NNIs). Nucleoside analogs are anabolized to active triphosphates that act as alternative substrates for the polymerase and non-nucleoside inhibitors (NNIs) bind to allosteric regions on the protein. Nucleoside or nucleotide inhibitors mimic natural polymerase substrates and act as chain terminators. They inhibit the initiation of RNA transcription and elongation of a nascent RNA chain.
In addition to targeting RNA polymerase, other RNA viral proteins may also be targeted in combination therapies. For example, HCV proteins that are additional targets for therapeutic approaches are NS3/4A (a serine protease) and NS5A (a non-structural protein that is an essential component of HCV replicase and exerts a range of effects on cellular pathways).
In December 2013, the first nucleoside NS5B polymerase inhibitor sofosbuvir (Sovaldi®, Gilead Sciences) was approved. Sovaldi® is a uridine phosphoramidate prodrug that is taken up by hepatocytes and undergoes intracellular activation to afford the active metabolite, 2′-deoxy-2′-α-fluoro-β-C-methyluridine-5′-triphosphate.

Sovaldi® is the first drug that has demonstrated safety and efficacy to treat certain types of HCV infection without the need for co-administration of interferon. Sovaldi® is the third drug with breakthrough therapy designation to receive FDA approval.
In 2014, the U.S. FDA approved Harvoni® (ledispasvir, a NS5A inhibitor, and sofosbuvir) to treat chronic hepatitis C virus Genotype 1 infection. Harvoni® is the first combination pill approved to treat chronic HCV Genotype 1 infection. It is also the first approved regimen that does not require administration with interferon or ribavirin. In addition, the FDA approved simeprevir (Olysio™) in combination with sofosbuvir (Sovaldi®) as a once-daily, all oral, interferon and ribavirin-free treatment for adults with Genotype 1 HCV infection.
The U.S. FDA also approved AbbVie's VIEKIRA Pak™ in 2014, a multi-pill pack containing dasabuvir (a non-nucleoside NS5B polymerase inhibitor), ombitasvir (a NS5A inhibitor), paritaprevir (a NS3/4A inhibitor), and ritonavir. The VIEKIRA Pak™ can be used with or without the ribavirin to treat Genotype 1 HCV infected patients including patients with compensated cirrhosis. VIEKIRA Pak™ does not require interferon co-therapy.
In July 2015, the U.S. FDA approved Technivie™ and Daklinza™ for the treatment of HCV genotype 4 and HCV Genotype 3, respectively. Technivie™ (Ombitasvir/paritaprevir/ritonavir) was approved for use in combination with ribavirin for the treatment of HCV genotype 4 in patients without scarring and cirrhosis and is the first option for HCV-4 infected patients who do not require co-administration with interferon. Daklinza™ was approved for use with Sovaldi® to treat HCV genotype 3 infections. Daklinza™ is the first drug that has demonstrated safety and efficacy in treating HCV Genotype 3 without the need for co-administration of interferon or ribavirin.
In October 2015, the U.S. FDA warned that HCV treatments Viekira Pak and Technivie can cause serious liver injury primarily in patients with underlying advanced liver disease and required that additional information about safety be added to the label.
Other current approved therapies for HCV include interferon alpha-2b or pegylated interferon alpha-2b)(Pegintron®), which can be administered with ribavirin (Rebetol®), NS3/4A telaprevir (Incivek®, Vertex and Johnson & Johnson), boceprevir (Victrelis™, Merck), simeprevir (Olysio™, Johnson & Johnson), paritaprevir (AbbVie), Ombitasvir (AbbVie), the NNI Dasabuvir (ABT-333) and Merck's Zepatier™ (a single-tablet combination of the two drugs grazoprevir and elbasvir).
Additional NS5B polymerase inhibitors are currently under development. Merck is developing the uridine nucleotide prodrug MK-3682 (formerly Idenix IDX21437) and the drug is currently in Phase II combination trials.
United States patents and WO applications that describe nucleoside polymerase inhibitors for the treatment of Flaviviridae, including HCV, include those filed by Idenix Pharmaceuticals (U.S. Pat. Nos. 6,812,219; 6,914,054; 7,105,493; 7,138,376; 7,148,206; 7,157,441; 7,163,929; 7,169,766; 7,192,936; 7,365,057; 7,384,924; 7,456,155; 7,547,704; 7,582,618; 7,608,597; 7,608,600; 7,625,875; 7,635,689; 7,662,798; 7,824,851; 7,902,202; 7,932,240; 7,951,789; 8,193,372; 8,299,038; 8,343,937; 8,362,068; 8,507,460; 8,637,475; 8,674,085; 8,680,071; 8,691,788, 8,742,101, 8,951,985; 9,109,001; 9,243,025; US2016/0002281; US2013/0064794; WO/2015/095305; WO/2015/081133; WO/2015/061683; WO/2013/177219; WO/2013/039920; WO/2014/137930; WO/2014/052638; WO/2012/154321); Merck (U.S. Pat. Nos. 6,777,395; 7,105,499; 7,125,855; 7,202,224; 7,323,449; 7,339,054; 7,534,767; 7,632,821; 7,879,815; 8,071,568; 8,148,349; 8,470,834; 8,481,712; 8,541,434; 8,697,694; 8,715,638, 9,061,041; 9,156,872 and WO/2013/009737); Emory University (U.S. Pat. Nos. 6,348,587; 6,911,424; 7,307,065; 7,495,006; 7,662,938; 7,772,208; 8,114,994; 8,168,583; 8,609,627; US 2014/0212382; and WO2014/1244430); Gilead Sciences/Pharmasset Inc. (U.S. Pat. Nos. 7,842,672; 7,973,013; 8,008,264; 8,012,941; 8,012,942; 8,318,682; 8,324,179; 8,415,308; 8,455,451; 8,563,530; 8,841,275; 8,853,171; 8,871,785; 8,877,733; 8,889,159; 8,906,880; 8,912,321; 8,957,045; 8,957,046; 9,045,520; 9,085,573; 9,090,642; and 9,139,604) and (6,908,924; 6,949,522; 7,094,770; 7,211,570; 7,429,572; 7,601,820; 7,638,502; 7,718,790; 7,772,208; RE42,015; U.S. Pat. Nos. 7,919,247; 7,964,580; 8,093,380; 8,114,997; 8,173,621; 8,334,270; 8,415,322; 8,481,713; 8,492,539; 8,551,973; 8,580,765; 8,618,076; 8,629,263; 8,633,309; 8,642,756; 8,716,262; 8,716,263; 8,735,345; 8,735,372; 8,735,569; 8,759,510 and 8,765,710); Hoffman La-Roche (U.S. Pat. No. 6,660,721), Roche (U.S. Pat. Nos. 6,784,166; 7,608,599, 7,608,601 and 8,071,567); Alios BioPharma Inc. (U.S. Pat. Nos. 8,895,723; 8,877,731; 8,871,737, 8,846,896, 8,772,474; 8,980,865; 9,012,427; US 2015/0105341; US 2015/0011497; US 2010/0249068; US2012/0070411; WO 2015/054465; WO 2014/209979; WO 2014/100505; WO 2014/100498; WO 2013/142159; WO 2013/142157; WO 2013/096680; WO 2013/088155; WO 2010/108135), Enanta Pharmaceuticals (U.S. Pat. Nos. 8,575,119; 8,846,638; 9,085,599; WO 2013/044030; WO 2012/125900), Biota (U.S. Pat. Nos. 7,268,119; 7,285,658; 7,713,941; 8,119,607; 8,415,309; 8,501,699 and 8,802,840), Biocryst Pharmaceuticals ( U.S. Pat. Nos. 7,388,002; 7,429,571; 7,514,410; 7,560,434; 7,994,139; 8,133,870; 8,163,703; 8,242,085 and 8,440,813), Alla Chem, LLC (U.S. Pat. No. 8,889,701 and WO 2015/053662), Inhibitex (U.S. Pat. No. 8,759,318 and WO/2012/092484), Janssen Products (U.S. Pat. Nos. 8,399,429; 8,431,588, 8,481,510, 8,552,021, 8,933,052; 9,006,29 and 9,012,428) the University of Georgia Foundation (U.S. Pat. Nos. 6,348,587; 7,307,065; 7,662,938; 8,168,583; 8,673,926, 8,816,074; 8,921,384 and 8,946,244), RFS Pharma, LLC (U.S. Pat. Nos. 8,895,531; 8,859,595; 8,815,829; 8,609,627; 7,560,550; US 2014/0066395; US 2014/0235566; US 2010/0279969; WO/2010/091386 and WO 2012/158811) University College Cardiff Consultants Limited (WO/2014/076490, WO 2010/081082; WO/2008/062206), Achillion Pharmaceuticals, Inc. (WO/2014/169278 and WO 2014/169280), Cocrystal Pharma, Inc. (U.S. Pat. No. 9,173,893), Katholieke Universiteit Leuven (WO 2015/158913), Catabasis (WO 2013/090420) and the Regents of the University of Minnesota (WO 2006/004637).
Atea Pharmaceuticals, Inc. has disclosed β-D-2′-deoxy-2′-α-fluoro-2′-β-C-substituted-2-modified-N6-(mono- and di-methyl) purine nucleotides for the treatment of HCV in U.S. Pat. No. 9,828,410 and PCT Application No. WO 2016/144918. Atea has also disclosed β-D-2′-deoxy-2′-substituted-4′-substituted-2-N6-substituted-6-aminopurine nucleotides for the treatment of paramyxovirus and orthomyxovirus infections in US 2018/0009836 and WO 2018/009623.
There remains a strong medical need to develop anti-HCV therapies that are safe, effective and well-tolerated. The need is accentuated by the expectation of drug resistance. More potent direct-acting antivirals could significantly shorten treatment duration and improve compliance and SVR (sustained viral response) rates for patients infected with all HCV genotypes.
It is therefore an object of the present invention to provide compounds, pharmaceutical compositions, methods, and dosage forms to treat and/or prevent infections of HCV.